Chemical-mechanical polishing (“CMP”) processes are used in the manufacturing of microelectronic devices to form flat surfaces on semiconductor wafers, field emission displays, and many other microelectronic substrates. For example, the manufacture of semiconductor devices generally involves the formation of various process layers, selective removal or patterning of portions of those layers, and deposition of yet additional process layers above the surface of a semiconducting substrate to form a semiconductor wafer. The process layers can include, by way of example, insulation layers, gate oxide layers, conductive layers, and layers of metal or glass, etc. It is generally desirable in certain steps of the wafer process that the uppermost surface of the process layers be planar, i.e., flat, for the deposition of subsequent layers. CMP is used to planarize process layers wherein a deposited material, such as a conductive or insulating material, is polished to planarize the wafer for subsequent process steps.
In a typical CMP process, a wafer is mounted upside down on a carrier in a CMP tool. A force pushes the carrier and the wafer downward toward a polishing pad. The carrier and the wafer are rotated above the rotating polishing pad on the CMP tool's polishing table. A polishing composition (also referred to as a polishing slurry) generally is introduced between the rotating wafer and the rotating polishing pad during the polishing process. The polishing composition typically contains a chemical that interacts with or dissolves portions of the uppermost wafer layer(s) and an abrasive material that physically removes portions of the layer(s). The wafer and the polishing pad can be rotated in the same direction or in opposite directions, whichever is desirable for the particular polishing process being carried out. The carrier also can oscillate across the polishing pad on the polishing table.
In polishing the surface of a wafer, it is often advantageous to monitor the polishing process in situ. One method of monitoring the polishing process in situ involves the use of a polishing pad having an aperture or window. The aperture or window provides a portal through which light can pass to allow the inspection of the wafer surface during the polishing process. Polishing pads having apertures and windows are known and have been used to polish substrates, such as the surface of semiconductor devices. For example, U.S. Pat. No. 5,605,760 provides a pad having a transparent window formed from a solid, uniform polymer, which has no intrinsic ability to absorb or transport slurry. U.S. Pat. No. 5,433,651 discloses a polishing pad wherein a portion of the pad has been removed to provide an aperture through which light can pass. U.S. Pat. Nos. 5,893,796 and 5,964,643 disclose removing a portion of a polishing pad to provide an aperture and placing a transparent polyurethane or quartz plug in the aperture to provide a transparent window, or removing a portion of the backing of a polishing pad to provide a translucency in the pad. U.S. Pat. Nos. 6,171,181 and 6,387,312 disclose a polishing pad having a transparent region that is formed by solidifying a flowable material (e.g., polyurethane) at a rapid rate of cooling.
One problem often encountered during chemical-mechanical polishing is the tendency for abrasive particles from the polishing composition to adhere to or scratch the surface of the polishing pad window. The presence of scratches or polishing composition on the polishing pad window can obstruct transmission of light through the window thereby reducing the sensitivity of the optical endpoint detection method. Recessing the window from the surface of the polishing pad can reduce the amount of scratching of the window. However, the recess also provides a cavity into which polishing composition can flow and become trapped. U.S. Pat. No. 6,254,459 suggests coating the first surface of the window with a slurry-phobic material. Similarly, U.S. Pat. No. 6,395,130 suggests the use of hydrophobic light pipes and windows to resist accumulation of polishing composition thereon. U.S. patent application Publication 2003/0129931 A1 similarly suggests coating the polishing pad window in an anti-fouling resin, such as a fluorine-based polymer containing a polysiloxane segment.
Although several of the above-described polishing pads are suitable for their intended purpose, a need remains for other polishing pads that provide effective planarization coupled with effective optical endpoint detection, particularly in chemical-mechanical polishing of a substrate. In addition, there is a need for polishing pads having satisfactory features such as polishing efficiency, slurry flow across and within the polishing pad, resistance to corrosive etchants, and/or polishing uniformity. Finally, there is a need for polishing pads that can be produced using relatively low cost methods and which require little or no conditioning prior to use.
The invention provides such a polishing pad. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.